Campi Flegrei and the sunken city of Baia

West of Naples the ground breathes. It rises and falls by metres over centuries, and somewhere along the way it took the most fashionable resort in the Roman empire down with it.

Baia is now on the seabed, in shallow water, and you can look at it through the floor of a boat.

The visit

• Sunken Baia — the villas, streets, mosaic floors and statue bases of the town where Roman senators kept their seaside houses, now lying at eight to ten metres. A glass-bottomed boat covers it in about an hour; if you dive or snorkel, you can go down to it with a licensed guide, which has to be booked well in advance
• The Flavian amphitheatre at Pozzuoli — the third largest in Italy after the Colosseum and Capua, and the one where you can walk the entire underground level, the machinery floor, which at the Colosseum you mostly cannot. There is usually nobody there
• The Piscina Mirabilis — a Roman cistern the size of a cathedral, cut into the rock to supply the imperial fleet at Misenum. Forty-eight pillars, an echo, and almost no visitors
• The Castle of Baia and its museum, where the pieces lifted out of the water are kept, including the reassembled nymphaeum of the emperor Claudius
• On request, Pozzuoli’s Jewish thread — this was Puteoli, the port where ships from Alexandria and Judaea landed. Josephus records Jews here in the first century, which makes it one of the earliest Jewish presences documented in Italy outside Rome itself

Making the day work

The Phlegraean Fields are twenty to thirty minutes west of Naples, and the sites are spread out, so this is a car day rather than a walking one.

• Half a day covers the boat over Baia plus one or two of the land sites. A full day covers all of them without hurrying
• The boat depends on the sea. In flat water you see a great deal; in chop you see very little, so the day is planned with an alternative ready rather than a promise
• Diving is possible at a maximum of eight to ten metres, guided by an authorised underwater archaeological guide, and must be arranged weeks ahead
• It is the natural second day for anyone who has already done Naples and Pompeii and wants Roman Campania without the crowds
• No kosher food exists anywhere out here. As everywhere in the south, meals are arranged in advance through the synagogue in Naples or carried with you

Questions people ask

Can you actually see the sunken city of Baia?
Yes. It lies in eight to ten metres of water and is visited either by glass-bottomed boat, which takes about an hour, or by snorkelling and diving with a licensed underwater guide. What you see depends entirely on how calm the sea is that day.

Why did Baia sink?
Bradyseism — the slow rising and falling of the ground in the volcanic caldera west of Naples. Over centuries it carried the shoreline, and the Roman resort built along it, below sea level.

Is the Pozzuoli amphitheatre worth visiting?
It is the third largest in Italy, and unlike the Colosseum its underground level is almost entirely open to walk through. It is rarely busy.

Do you need to dive to see it?
No. The glass-bottomed boat covers the same ground in an hour with no equipment and no experience needed.

Is there a Jewish connection to Pozzuoli?
Yes. As Puteoli it was the great port for ships from the eastern Mediterranean, and Josephus records a Jewish presence there in the first century, making it one of the earliest documented outside Rome.